Table 3: Intra- and inter-observer statistics for average screw angle and maximum screw angle for patients assessed (O: Observer Number 1; R: Observer Number 2).

Observer and screw	ICC¹	Raw Slope²	mean difference³	95% Limits of agreement⁴	rho⁵	Pitman's test⁶ P	Bradley-Blackwood test⁷ P
Observer and screw	ICC¹	(intercept)	(95% CI)	95% Limits of agreement⁴	rho⁵	Pitman's test⁶ P	Bradley-Blackwood test⁷ P
Intra-observer measurement 1 v 2
O average	0.99	1.031 (-0.01)	0.09 (-0.10-0.28)	-1.32 - 1.49	0.223	0.095	0.16
R average	0.939	1.040 (-0.42)	-0.29 (-0.78-0.20)	-3.88 - 3.30	0.116	0.39	0.34
O max	0.993	1.025 (0.09)	0.24 (0.03-0.45)	-1.34 - 1.81	0.223	0.089	0.02
R max	0.946	0.986 (-0.54)	-0.63 (-1.20 - -0.05)	-4.94 - 3.69	-0.044	0.74	0.1
Inter-observer R v O
Average	0.979	0.997 (0.07)	0.06 (-0.22-0.34)	-2.01 - 2.13	-0.014	0.92	0.92
Maximum	0.98	1.042 (-0.04)	0.20 (-0.16-0.57)	-2.52 - 2.93	0.211	0.11	0.15

¹Inter-class correlation co-efficient between observation 1 and observation 2; ²Perfect agreement between the two observations would give slope = 1; intercept = 0; ³Mean difference between the two observations made from each patient; ⁴The reference range for difference between observations (according to Bland-Altman, 1986); ⁵The correlation coefficient for the association between the difference and mean as depicted in the Bland-Altman plots; ⁶Pitman's is a test for zero correlation between the sums and differences of the paired observations; ⁷Bradley-Blackwood test is a test for the equivalence of both the means and the variance of the differences between the paired observations.